This invention relates to a rechargeable organic electrolyte cell expected to be used as a power source for a variety of small sized electronic apparatuses.
So-called organic electrolyte cells, making use of lithium as the anode active material and an organic electrolyte as the electrolyte, are low in self-discharging, high in voltage and excellent in shelf life, so that they may be used with high operational reliability for a prolonged period of five to ten years. For this reason, they are used at present extensively in electronic time pieces or as a variety of memory backup power sources.
However, the presently used organic electrolyte cells are primary cells, such that their service life is terminated when used once so that they leave a lot to be desired especially from economic considerations.
For this reason, with the rapid progress in a variety of electronic apparatuses, a strong demand has been raised for rechargeable organic electrolyte cells that can be used conveniently and economically for a prolonged time, and many researches are being conducted for developing this type of cells.
In general, metal lithium, lithium alloys, such as Li-Al alloys, electroconductive polymer materials, such as polyacetylene or polypyrrole, doped with lithium ions, or intercalation compounds with lithium ions mixed into crystals thereof, are used as the anodic material of the cell, while an organic electrolytic solution is used as the electrolyte thereof.
On the other hand, various materials have been proposed as the cathodic active material. Examples of these materials include TiS.sub.2, MoS.sub.2, NbSe.sub.2 or V.sub.2 O.sub.5, as disclosed in the Japanese Laid-Open Patent Publication No. 54836/1975.
The discharging reaction of the cell making use of these materials proceeds as the lithium ions of the anode are intercalated into the spacings between these materials, whereas the charging reaction proceeds as the lithium ions are deintercalated from these spacings towards the anode. In other words, the charging and discharging proceeds by a repetition of the reactions in which the lithium ions of the anode make entrance into and exit from the interlayer spacings of the cathode active material. For example, when using TiS.sub.2 as the cathode active material, the charging and discharging reaction may be represented by the formula ##STR1##
With the conventional cathodic material, charging and discharging proceeds by the above reaction. However, the conventional cathodic material has a deficiency that, with the repetition of the charging and discharging reactions, the discharge capacity thereof is decreased gradually. It is because the lithium ions, once having made an entrance into the cathode active material, tend to exit therefrom only with increased difficulties, such that only a limited fraction of the lithium ions having made an entrance into the cathode active material by discharging are returned towards the anode by the charging reaction. In other words, the lithium ions are caused to remain in the cathode in the form of Li.sub.x TiS.sub.2 so that the number of the lithium ions taking part in the ensuing charging reaction is decreased. The result is that the discharge capacity of the cell after the charging is decreased and the cyclic service life characteristics of the cell are correspondingly lowered.